This invention relates to an instrument for preparing the proximal femur to receive a proximal femoral prosthesis. The instrument is a combination of a novel handle assembly for securely holding a trial prosthesis/rasp which is used to prepare the femur. The handle assembly is then removed leaving the trial prosthesis/rasp in the femur to accomplish trial reduction of the hip joint.
During hip surgery involving the replacement of the proximal femoral head using a proximal femoral prosthesis, the proximal femur must be prepared to receive the stem of the proximal femoral prosthesis. A number of techniques have been developed to accomplish the insertion of such prosthesis, and such techniques typically involve the use of a rasp to accomplish the shaping of the proximal femur. Some techniques employ a rasp attached to a handle which is only used to prepare a socket in the proximal femur. A separate trial prosthesis is then inserted in the socket to accomplish reduction (i.e., proper sizing of a permanent femoral implant).
To achieve the best fixation of the permanent femoral implant, it has become a common practice to employ a combination femoral trial prosthesis/rasp to prepare the socket. The trial prosthesis/rasp is then left in the socket and a femoral prosthesis head is placed on a post extending from the trial prosthesis/rasp to accomplish reduction. The post may also be used to assist in preparation of the calcar surface. The trial prosthesis/rasp is then removed and a permanent femoral prosthesis is inserted into the prepared socket which remains basically unchanged since the rasping procedure was completed.
A number of instruments to hold the trial prosthesis/rasp have been suggested. It is important that the trial prosthesis/rasp be held rigidly. U.S. Pat. No. 4,306,550 to Forte (issued Dec. 22, 1981) shows a handle containing a releasable chuck to engage the post on the trial prosthesis/rasp. Other instruments using handles with chucks to hold the trial prosthesis/rasp are shown on pages 19-23 of a brochure entitled "The Total System" from Zimmer U.S.A., Inc. of Warsaw, IN and in item 16 (Art. Nr. 5104) in a Brochure entitled "Trunnion-head total hip, operative technique" from ALLO PRO AG, Dorfstrasse 13, CH-6340 Baar/Zug. These chuck-type instruments are somewhat complicated to manufacture.
As part of "The PCA.TM. Total Hip System", the Orthopaedics Division of Howmedica, Inc. of Rutherford, N.J. sells a Broach/Trial Stem Handle (Catalog No. 6079-0-000) for use with Broach/Trial Stems (Catalog Nos. 6079-0-001) to -007 and 6080-0-001 to -007) wherein the Handle receives the trunnion (post) on the Stem within a coupler which is closed by means of a moveable arm and held shut by moving the arm against the handle forming the main body. The coupler also has a pin extending from its end which appears to engage with the upper part of the Stem on which the part is located. Howmedica, Inc. also sells a Femoral Stem Extractor (Catalog No. 6079-6-400) which appears to be a locking set of pliers which is used to extract a femoral prosthesis stem from the femur, but does not appear to be useful for inserting a femoral trial prosthesis/rasp. These Howmedica devices are described on pages 8, 14-17, and 43 of their brochure number H4139 15M 1/84 B and on pages 42-49 of the surgical procedure (FIGS. 38a-44) found between pages 38 and 39 of that brochure.
Instruments employing screw-lock or push-pin mechanisms to affix the trial prosthesis-rasp to the handle are shown in brochure no. Y-BMT-010/090183 entitled "CFE TAPERLOC Hip System Surgical Technique" from Biomet, Inc. of Warsaw, IN (spring-loaded button), and in brochure no. 20M1183 0611-52 entitled "the AML.TM. Total Hip System with Porocoat.RTM." as Broach Handle 2002-22 from DePuy, Inc. of Warsaw, IN (screw-lock). A femoral trial prosthesis and prosthesis Introducer/Extractor (Catalog No. JA 101) employing a locking pin which passes through the handle and the prosthesis is shown on page 90 (pages 43 and 44 show its use) of a brochure entitled "The Poro Metal cementless total hip prosthesis" distributed by Daumer International, P.O. Box 2229, 5632 Wermelskirchen, West Germany (page 91 shows a Catalog No. JA 601 reamer which is not detachable or useful as a trial prosthesis).
U.S. Pat. No. 3,818,514 to Clark (issued June 25, 1974) shows a protective sheath for a femoral prosthesis head which employs a sheath lined with a compressible material which fits about the prosthesis neck and possibly the head to securely engage the prosthesis and to aid in the insertion of the prosthesis into a prepared socket in the proximal femur. The compressible material prevents damage to the head when the prosthesis is pounded into the socket, but does allow the prosthesis to move relative to the sheath.
There is still a need for an instrument which will hold a femoral trial prosthesis/rasp rigidly in place during use, but which permits simple engagement and disengagement of the trial prosthesis/rasp.